A continuing desire to reduce dependency on petroleum as an energy source and to reduce fuel emissions has provoked intense interest in fuel cells as alternative energy sources. Briefly, a fuel cell produces electricity generated from the oxidation of hydrogen, the fuel of the cell. Fuel cells include an anode through which hydrogen gas is passed. The hydrogen is oxidized to hydrogen ions, and electrons from the oxidation are delivered via an external circuit to the cell cathode where they combine with oxygen to produce oxygen anions. Hydrogen ions generated in the anode chamber flow through a proton exchange membrane (PEM) to the to the cathode chamber where they combine with the oxygen anions to produce water.
In order to obtain usable voltages for various applications, a stack of about 100-200 cells in series is generally, required. These cell stacks require bipolar plates, which perform several functions: they allow the conduction of electrons between fuel cells with minimal electrical resistance; they prevent the transfer of materials between fuel cells; they also provide a flow structure for gas distribution in a fuel cell. Importantly, fuel cells form corrosive solutions with which bipolar plates are in constant contact. Any corrosion products resulting from contact would contaminate the PEM and increase the internal resistance of the cell and decrease the cell lifetime. Therefore, bipolar plates should be highly corrosion resistant. In addition, bipolar plates contribute a significant fraction of the cost of a fuel cell, and the development of low cost bipolar plates and those materials used to produce them is a significant challenge for commercialization of PEM fuel cells.
The corrosion properties of materials can be tested using a corrosion test cell. One such cell has been described in U. S. Pat. No. 4,049,525 to D. R. Dutton and T. C. Musolf entitled xe2x80x9cCorrosion Test Cellxe2x80x9d, which issued Sep. 20, 1977. This cell tests metal rods for corrosion, and can test several simultaneously. This test cell includes an electrically non-conductive vessel, a corrosive electrolyte solution in the vessel, and reference and auxiliary electrodes immersed in the solution. One end of each rod is attached to an electrode that is immersed in the electrolyte solution. The other end of the rod is outside the vessel, and is attached to a device that records the potentiodymanic anodic polarization curve for that particular rod. The middle of the rod is insulated from the solution with Teflon(trademark).
A paper to R. L. Borop and N. E. Vanderborgh entitled xe2x80x9cDesign and Testing Criteria for Bipolar Plate Materials for PEM Fuel Cell Applicationsxe2x80x9d, which appeared in Mat. Res. Soc. Symp. Proc. Vol. 393, (1995), suggests various materials that could be useful for bipolar plates.
A paper by L. Ma, S. Warthesen, and D. A. Shores entitled xe2x80x9cEvaluation of Materials for Bipolar Plates in PEMFCsxe2x80x9d, in Proc. Symp. On New Materials for Electrochemical Systems (1999) evaluates the performance of several corrosion resistant alloys for bipolar plates.
The practical development of fuel cells includes the development of optimal bipolar plate materials. Corrosion test cell for evaluating the corrosion properties of bipolar plate materials is therefore highly desirable. Therefore, an object of the present invention is to provide a corrosion test cell for testing the performance of bipolar plates.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as embodied and broadly described herein, the present invention includes a corrosion test cell for evaluating corrosion resistance in fuel cell bipolar plates is described. The cell has a transparent or translucent cell body having a pair of identical cell body members that seal against opposite sides of a bipolar plate. The cell includes an anode chamber and a cathode chamber, each on opposite sides of the plate. Each chamber contains a pair of mesh platinum current collectors and a catalyst layer pressed between current collectors and the plate. Each chamber is filled with an electrolyte solution that is replenished with fluid from a much larger electrolyte reservoir. The cell includes gas inlets to each chamber for hydrogen gas and air. As the gases flow into a chamber, they pass along the platinum mesh, through the catalyst layer, and to the bipolar plate. The gas exits the chamber through passageways that provide fluid communication between the anode and cathode chambers and the reservoir, and exits the test cell through an exit port in the reservoir. The flow of gas into the cell produces a constant flow of fresh electrolyte into each chamber. Openings in each cell body member allow reference electrodes to enter the cell body and contact the electrolyte in the reservoir therein. During operation, while hydrogen gas is passed into one chamber and air into the other chamber, the cell resistance is measured, which is used to evaluate the corrosion properties of the bipolar plate.